diff --git a/libraries/AP_HAL_AVR/SPIDevice_SPI0.cpp b/libraries/AP_HAL_AVR/SPIDevice_SPI0.cpp
index b26fb7ca33..ecde45095b 100644
--- a/libraries/AP_HAL_AVR/SPIDevice_SPI0.cpp
+++ b/libraries/AP_HAL_AVR/SPIDevice_SPI0.cpp
@@ -69,6 +69,32 @@ inline uint8_t AVRSPI0DeviceDriver::_transfer(uint8_t data) {
     return read_spdr;
 }
 
+/**
+   a specialised transfer function for the MPU6k. This saves 2 usec
+   per byte
+ */
+void AVRSPI0DeviceDriver::_transfer15(const uint8_t *tx, uint8_t *rx) 
+{
+    spi0_transferflag = true;
+#define TRANSFER1(i) do { SPDR = tx[i];  while(!(SPSR & _BV(SPIF))); rx[i] = SPDR; } while(0)
+    TRANSFER1(0);
+    TRANSFER1(1);
+    TRANSFER1(2);
+    TRANSFER1(3);
+    TRANSFER1(4);
+    TRANSFER1(5);
+    TRANSFER1(6);
+    TRANSFER1(7);
+    TRANSFER1(8);
+    TRANSFER1(9);
+    TRANSFER1(10);
+    TRANSFER1(11);
+    TRANSFER1(12);
+    TRANSFER1(13);
+    TRANSFER1(14);
+    spi0_transferflag = false;
+}
+
 void AVRSPI0DeviceDriver::transfer(const uint8_t *tx, uint16_t len) {
     for (uint16_t i = 0; i < len; i++) {
             _transfer(tx[i]);
@@ -83,6 +109,12 @@ void AVRSPI0DeviceDriver::transaction(const uint8_t *tx, uint8_t *rx,
             _transfer(tx[i]);
         }
     } else {
+        while (len >= 15) {
+            _transfer15(tx, rx);
+            tx += 15;
+            rx += 15;
+            len -= 15;
+        }
         for (uint16_t i = 0; i < len; i++) {
             rx[i] = _transfer(tx[i]);
         }
diff --git a/libraries/AP_HAL_AVR/SPIDevice_SPI2.cpp b/libraries/AP_HAL_AVR/SPIDevice_SPI2.cpp
index 97b85fc75f..6080c2fbc9 100644
--- a/libraries/AP_HAL_AVR/SPIDevice_SPI2.cpp
+++ b/libraries/AP_HAL_AVR/SPIDevice_SPI2.cpp
@@ -69,6 +69,34 @@ inline uint8_t AVRSPI2DeviceDriver::_transfer(uint8_t data) {
     return UDR2;
 }
 
+/**
+   a specialist transfer function for the APM1 ADC
+ */
+void AVRSPI2DeviceDriver::_transfer17(const uint8_t *tx, uint8_t *rx) 
+{
+#define TRANSFER1(i) do { while ( !( UCSR2A & _BV(UDRE2)) ); \
+        UDR2 = tx[i]; \
+        while ( !(UCSR2A & _BV(RXC2)) ) ; \
+        rx[i] = UDR2; } while (0)
+    TRANSFER1(0);
+    TRANSFER1(1);
+    TRANSFER1(2);
+    TRANSFER1(3);
+    TRANSFER1(4);
+    TRANSFER1(5);
+    TRANSFER1(6);
+    TRANSFER1(7);
+    TRANSFER1(8);
+    TRANSFER1(9);
+    TRANSFER1(10);
+    TRANSFER1(11);
+    TRANSFER1(12);
+    TRANSFER1(13);
+    TRANSFER1(14);
+    TRANSFER1(15);
+    TRANSFER1(16);
+}
+
 void AVRSPI2DeviceDriver::transaction(const uint8_t *tx, uint8_t *rx,
         uint16_t len) {
     _cs_assert();
@@ -77,6 +105,12 @@ void AVRSPI2DeviceDriver::transaction(const uint8_t *tx, uint8_t *rx,
             _transfer(tx[i]);
         }
     } else {
+        while (len >= 17) {
+            _transfer17(tx, rx);
+            tx += 17;
+            rx += 17;
+            len -= 17;
+        }
         for (uint16_t i = 0; i < len; i++) {
             rx[i] = _transfer(tx[i]);
         }
diff --git a/libraries/AP_HAL_AVR/SPIDevices.h b/libraries/AP_HAL_AVR/SPIDevices.h
index 800b0f4231..4429c72fdd 100644
--- a/libraries/AP_HAL_AVR/SPIDevices.h
+++ b/libraries/AP_HAL_AVR/SPIDevices.h
@@ -31,6 +31,8 @@ private:
     void _cs_assert();
     void _cs_release();
     uint8_t _transfer(uint8_t data);
+    // used for MPU6k
+    void _transfer15(const uint8_t *tx, uint8_t *rx);
 
     static AP_HAL_AVR::AVRSemaphore _semaphore;
 
@@ -66,6 +68,8 @@ private:
     void _cs_assert();
     void _cs_release();
     uint8_t _transfer(uint8_t data);
+    // used for APM1 ADC
+    void _transfer17(const uint8_t *tx, uint8_t *rx);
 
     static AP_HAL_AVR::AVRSemaphore _semaphore;